Membrane keyboards are used in high-tech devices in medical equipment, mobile phones, electrical household appliances, cash dispensers, remote controls as well as in industrial machines. The demands on the quality and reliability of keyboard elements is high and is on the rise. Keyboards must always remain operational no matter what special conditions they are subjected to and they must be capable of resisting external impacts such as moisture and soiling. Flexibility plus ease of cleaning and high resistance are the key criteria that have to be met.
As a rule membrane keyboards are made up of several individual layers, normally four. These are placed on top of each other and so constitute the overall structure of the control elements. The top layer is called the overlay and is very often made of polycarbonate or polyester. The rear side of the foil is printed, in order to ensure the best possible protection against abrasion. The typical application used here is screen printing, although a sharp rise in the use of digital printing can be observed in this industrial segment due to the need for flexibility. The switch foils are located directly under the overlay. The front and switch foils are separated by a so-called spacer foil to accommodate the switch domes. These are usually made of polyester, but also polyamide. The conductive tracks and switch points or contact surfaces are located on the switch foil.
Processing of membrane keyboards:
Punches or water-jet, knife or laser cutters are often used. Punching is still the fastest way to outline foil products. Depending on the product value, punches are a very cost-effective solution for medium and large series. But how productive is the use of punches for single items and small series? The expensive production of the cutting die is what pushes costs up here and makes production unprofitable. The same applies where immediate delivery is required and when the properties of individual products change continuously. In such cases punching is not a feasible option for production.
Water-jet cutting systems, on the other hand, quickly reach their limits where high cutting accuracy is concerned. Soiling and excessive moisture on the material being processed are, of course, also the natural consequences of using water. Compared to punch and water-jet technologies, knives are subject to wear and this in turn compromises continuity in quality. Follow-up costs for tool replacement and the machine downtimes this involves are inevitable.
Laser cutting scores points where accuracy is concerned. But it has another even more interesting special advantage – cutting with no contact whatsoever with the material. Cutting with a laser beam is a completely contactless process. Foil remnants and adhesives cannot stick to the tool, the material does not need to be fixed and there is no crushing or flaking of the material. The thermal process can fuse the cut edges, in other words it has a kind of sealing effect. Automatic protection against soiling without the need of any extra time and expense. All reasons why laser technology is used for foil-based control elements, especially where flexibility in production is concerned.